In some photonic devices, shifting the phase of an optical signal is desirable. Optical phase shifting may be used in optical modulators, switches, sensors, multiplexers, demultiplexers, and other devices. When light propagates through a media, it travels an optical path length that depends on the effective index of refraction of the media. The optical phase may be adjusted when light propagates through a media having a desired optical path length to adjust the optical phase.
Optical devices may be integrated in a photonic integrated circuit (PIC) containing optical waveguides. Optical waveguides are light conduits that contain a slab, strip, or cylinder of a dielectric material surrounded by another dielectric material having a lower refractive index. The light propagates along, and is confined to, the higher refractive index material through total internal reflection. In a PIC, the core may be silicon, surrounded by a lower refractive index material, such as silicon dioxide, silicon nitride, silicon oxynitride, and/or air. The waveguides may be a single mode or multi-mode waveguide. In an example, a PIC operates at a telecommunications wavelength, such as 1550 nm or 1310 nm. The light may be coupled into, out of, or between optical waveguides. In a PIC, multiple photonic functions are integrated on a substrate, such as silicon-on-insulator (SOI). PICs are used for optical communications, and for other applications, such as biomedical application sand photonic computing. PICs may provide increased functionality, while being compact, and enabling higher performance than discrete optical devices.